Occupied housing units are classified by the number of persons per room, calculated by dividing the number of persons by the number of rooms in each unit. In 1960, categories of persons per room tabulated were: 0.50 or less, 0.51 to 0.75, 0.76 to 1.00, 1.01 to 1.50, 1.51 or more; in 1970, the terminal category is broken down into 1.51 to 2.00, 2.01 or more. Persons per room data are used to determine overcrowding in housing units.

In 1960, the highest category for number of rooms was 10 or more, this was given an assumed mean value of 11. In 1970, the highest category is 9 rooms or more, given an assumed value of 10 in calculating averages.